Abstract Loss of homeostasis, defined as the dynamic maintenance of the internal environment within functionally tolerable limits, is understood as central to the initiation and progression of disease. The central objective of this proposal is to develop new insights into the mechanisms of homeostasis as it involves the brainstem nucleus tractus solitarius (NTS) and the role of the neuromodulator Angiotensin II (AngII) in hypertension. The NTS is a key integrative structure in the central neuronal orchestration of homeostasis, while AngII is one of the most pleiotropically active and therefore biomedically important molecules in mammalian biology. The NTS neuronal response to Ang II, acting through AT1R, involves processes that affect neuronal electrophysiology via the interplay of (1) membrane ion channels modulated via intracellular signaling, and (2) expression dynamics of multiple genes functioning in an interconnected network. Both of these contribute to the adaptive NTS response that contributes to the development and maintenance of changed homeostatic function in disease. The goal is for bridging from molecular level interaction networks to electrophysiological signal generation. The questions addressed here are fundamental for brain functioning and physiology; in particular, in connection to regulation of the response to various stimuli. To this end, we focus on the AT1R induced neuromodulation at two different temporal levels, in two Specific Aims. Aim 1, with focus on the AT1 receptor- to-signaling-to-electrophysiology, will develop a mathematical model of the rapid and transient modulation of membrane ion channel currents based on experimental data. This will support simulation study of the detailed interaction of signaling pathways and biophysical processes underlying short-to-intermediate timeframe adaptive electrophysiological activity patterns. Model predictions will be experimentally validated using pathway inhibitors and the results iteratively utilized in further model refinement. The focus of Aim 2 is to develop and experimentally validate a mathematical model of the regulatory network downstream of AT1R activation in NTS. To this end, we will follow a structured approach that we have previously developed to combine microarray gene expression data and promoter occupancy of key transcription factors. The network hypotheses will be experimentally validated using Chromatin ImmunoPrecipitation (ChIP)-based methods and the results will be used iteratively in further refinement of the regulatory network model. Successful completion of these Aims will provide the first systems level analysis of molecular mechanisms involved in the NTS adaptive response to AT1R activation, providing insights into the mechanisms of homeostasis. PUBLIC HEALTH RELEVANCE: Project Narrative Loss of homeostasis, defined as the dynamic maintenance of the internal environment within functionally tolerable limits, is understood as central to the initiation and progression of disease. The present project is based on the hypothesis that these processes arise from complex and dynamic neuronal processes that involve multiple signaling molecules and genes functioning over time in a hierarchical and interconnected network. We aim to combine computational models with experimental measurements in order to develop and validate hypotheses of the underlying molecular mechanisms.